Uncertainties of ENSO-related Regional Hadley Circulation Anomalies within Eight Reanalysis Datasets

El Nino-Southern Oscillation(ENSO),the leading mode of global interannual variability,usually intensifies the Hadley Circulation(HC),and meanwhile constrains its meridional extension,leading to an equatorward movement of the jet system.Previous studies have investigated the response of HC to ENSO events using different reanalysis datasets and evaluated their capability in capturing the main features of ENSO-associated HC anomalies.However,these studies mainly focused on the global HC,represented by a zonal-mean mass stream function(MSF).Comparatively fewer studies have evaluated HC responses from a regional perspective,partly due to the prerequisite of the Stokes MSF,which prevents us from integrating a regional HC.In this study,we adopt a recently developed technique to construct the three-dimensional structure of HC and evaluate the capability of eight state-of-the-art reanalyses in reproducing the regional HC response to ENSO events.Results show that all eight reanalyses reproduce the spatial structure of HC responses well,with an intensified HC around the central-eastern Pacific but weakened circulations around the Indo-Pacific warm pool and tropical Atlantic.The spatial correlation coefficient of the three-dimensional HC anomalies among the different datasets is always larger than 0.93.However,these datasets may not capture the amplitudes of the HC responses well.This uncertainty is especially large for ENSO-associated equatorially asymmetric HC anomalies,with the maximum amplitude in Climate Forecast System Reanalysis(CFSR)being about 2.7 times the minimum value in the Twentieth Century Reanalysis(20CR).One should be careful when using reanalysis data to evaluate the intensity of ENSO-associated HC anomalies.

Has the regional Hadley circulation over western Pacific during boreal winter been strengthening in recent decades?

Previous studies suggest a robust intensification of the zonally averaged hadley circulation(HC)during boreal winter in recent decades,but little is known regarding the regional HC.This study investigates long-term trends of the winter regional HC over the western pacific(WPHC)since 1979 using six reanalysis datasets.It is found that there are large discrepancies in the long-term trends of WPHC intensity among the six datasets.Specifically,three of the six reanalyses(erainterim,20CR and CFSR)show no discernible long-term trends,whereas NCEP-1,NCEP-2 and JRA-55 display pronounced intensification tendencies.Results in this study suggest that,although the warming trend of SST in the western tropical pacific identified in previous studies is robust,uncertainty remains regarding the long-term trends in the WPHC intensity.This raises a question about the factors involved in changes of the WPHC intensity.